1. Field of the Invention
The invention relates in general to a semiconductor structure and method for manufacturing the same, and more particularly to the semiconductor structure with high breakdown voltage and high resistance, and method for manufacturing the same.
2. Description of the Related Art
In the manufacture of semiconductor device, it is one of the important goals to construct a resistor with high resistance and ideal I-V curve. Semiconductor structures of FIG. 1 and FIG. 2 both schematically show P-well resistors; however, each possesses its own advantages and disadvantages. FIG. 1 is a cross-sectional view of a conventional resistor device. The conventional resistor 1 includes a P-substrate (ex: a P-type silicon substrate) 10, a N deep well 12 formed in the P-substrate 10, two P-wells 13a and 13b formed within the P-substrate 10 and respectively next to the N deep well 12, a P-well 14 formed within the N deep well 12, two P+ regions 17a and 17b formed within the P-well 14, and a N+ region 19 formed within the N deep well 12 and spaced apart from the P-well 14. Also, the P-wells 13a and 13b are implanted with a higher implant dosage than the P-well 14. Furthermore, a low voltage end (LV) is connected to the P+ region 17a, and a high voltage end (HV) is connected to the P+ region 17b and the N+ region 19 within the N deep well 12 for the purpose of preventing parasitic device (pnp) from being turned on at any moment.
FIG. 2 presents a typical I-V curve of the conventional resistor device of FIG. 1. For the structure of the resistor 1 of FIG. 1, junction breakdown typically happens at the interface between the N deep well 12 and the P-well 13a/13b. When the semiconductor structure 1 is operated at the voltage V1, junction breakdown happens and the current increases sharply, as shown in FIG. 2. According to the I-V curve of FIG. 2, the resistor 1 of FIG. 1 possesses “hard breakdown” characteristics. Typically, the operating voltage of the resistor 1 is less than voltage V1, the disadvantage of the resistor is that the resistance of the semiconductor structure 1 determined by the P-well 14 is relatively small.
FIG. 3 is a cross-sectional view of another conventional resistor device. The resistor 3 includes a P-substrate (ex: a P-type silicon substrate) 30, a N deep well 32 formed in the P-substrate 30, two P-wells 33a and 33b formed within the P-substrate 30 and respectively next to the N deep well 32, a P-body 35 formed within the N deep well 32, two P+ regions 37a and 37b formed within the P-body 35, and a N+ region 39 formed within the N deep well 32 and spaced apart from the P-body 35. The P-wells 33a and 33b are implanted with a higher implant dosage than the P-body 35 for a better insulation operation. Similarly, a low voltage end (LV) is connected to the P+ region 37a, and a high voltage end (HV) is connected to the P+ region 37b and the N+ region 39.
The differences between the resistors 1 and 3 are the portions for determining the resistance of the structure (i.e. the P-well 14 and the P-body 35). The implant dosage of the P-body 35 is lighter than the implant dosage of the P-well 14; therefore, the resistance of the semiconductor structure 3 is larger than the resistance of the semiconductor structure 1.
In the current applications, higher resistance of a fixed size resistor device and a high and hard-breakdown voltage are more favorable and practical. While the resistor can be smaller with higher resistance, and if the breakdown voltage is relatively higher, the application range will be wider with a higher operation voltage. Furthermore, it can be observed more easily and stable in the hard-breakdown voltage characteristic.
Although it is an attempt to manufacture a resistor with high resistance, the semiconductor structure 3 has several considerable problems, for example, not suitable for being operated at a high voltage. FIG. 4 presents a typical I-V curve of the conventional resistor device of FIG. 3. For the structure 3 of FIG. 3, junction breakdown typically happens at the interface between the P-body 35 and the P+ region 37a/37b. When the semiconductor structure 3 is operated between the voltage V2 and the voltage V2′, the current leakage is observed, and junction breakdown doesn't happen obviously until the operating voltage reaching the voltage V2′. According to the I-V curve of FIG. 4, the semiconductor structure 3 of FIG. 3 possesses “soft breakdown” characteristics which is undesirable in application. Typically, the operating voltage of the semiconductor structure 3 is less than voltage V2. Compared to the operating voltage of the semiconductor structure 1, voltage V2 is relatively smaller than voltage V1. Thus, the semiconductor structure 3 is not suitable for being operated at a high voltage.